Expressive Query Construction through Direct Manipulation of Nested Relational Results

Despite extensive research on visual query systems, the standard way to interact with relational databases remains to be through SQL queries and tailored form interfaces. We consider three requirements to be essential to a successful alternative: (1) query specification through direct manipulation of results, (2) the ability to view and modify any part of the current query without departing from the direct manipulation interface, and (3) SQL-like expressiveness. This paper presents the first visual query system to meet all three requirements in a single design. By directly manipulating nested relational results, and using spreadsheet idioms such as formulas and filters, the user can express a relationally complete set of query operators plus calculation, aggregation, outer joins, sorting, and nesting, while always remaining able to track and modify the state of the complete query. Our prototype gives the user an experience of responsive, incremental query building while pushing all actual query processing to the database layer. We evaluate our system with formative and controlled user studies on 28 spreadsheet users; the controlled study shows our system significantly outperforming Microsoft Access on the System Usability Scale.